A mobile phone is susceptible to minor but objectionable audio artifacts emanating from components within the mobile phone that are not part of the mobile phone""s audio system. One example of an objectionable audio artifact emanates from the electro-luminescent (EL) panel used for back-lighting a mobile phone""s display. Another example involves certain pulses generated by TDMA type RF communications devices. These artifacts can be particularly irritating even at low levels. Improved design practice can reduce but not eliminate these objectionable artifacts which typically sound like bees trapped inside the mobile phone.
Previously, there was no way to solve the objectionable artifact problem without increasing the sophistication of the mobile phone""s mechanical and/or acoustic design. Design solutions of this nature are achieved at increased cost, a longer product development cycle, and often result in decreased performance. Moreover, it is difficult to change the mechanical characteristics of a mobile phone but relatively easy to alter a few lines of digital signal processor (DSP) software code to generate a masking noise capable of counteracting the objectionable artifact.
What is needed is a method of masking objectionable artifacts in mobile phones without having to increase the sophistication of the mobile phone design.
Rather than attempting to eliminate objectionable artifacts in mobile phones completely, the present invention masks the objectionable artifacts with an appropriately constructed low level masking noise so that the objectionable artifacts are not detectable by the user of the mobile phone. It is often impractical to use the DSP to remove the artifact(s) because the DSP cannot obtain a sample of the artifact without a significant cost increase.
The present invention is a system and method of masking objectionable artifacts in a mobile telephone. The process starts by referring to the design characteristics of the mobile phone to determine the expected level and source of objectionable artifacts that will be apparent during operation of the mobile phone. The noise necessary to mask the objectionable artifacts is then calculated. The masking noise signal is then created within the mobile telephone and superimposed over the objectionable artifact.
The masking noise signal is typically created in a digital signal processor (DSP) resident within the mobile telephone using a pseudo-noise generator. The masking noise signal can be stored as a look-up table in the digital signal processor (DSP) of the mobile telephone.
To further enhance the effectiveness of the masking process, the masking noise signal is filtered to best match the objectionable artifact. The masking noise signal can be low pass filtered for objectionable artifacts that are lower in frequency. The masking noise signal can be high pass filtered for objectionable artifacts that are higher in frequency. Or, the masking noise signal can be band pass filtered for objectionable artifacts regardless of frequency.
In an alternative embodiment, the masking noise signal can be created as a band-limited masking noise signal within a pre-determined frequency bandwidth correlated to the frequency bandwidth of the objectionable artifact. In this embodiment, the noise masking signal has been pre-filtered and need not be filtered after it has been created.